How to scale UV map?
You do it the same way as everywhere else, by pressing S followed by the axis you want to scale on, i.e. X, Y or Z.

Additionally you can press S and then Shift + the axis you don't want to scale along, and thus scaling along the other two; So if you pressed S, followed by Shift + X, you would scale along Y and Z, but not X. This, however, only applies in the 3D View, not in the UV/Image Editor, as there are only two dimensions.